1. Field of the Invention
The present invention relates to a method for cooling a plurality of molten filaments comprised of a thermoplastic resin extruded from dies and to an apparatus for carrying out that method.
2. Description of the Related Art
FIG. 3 shows a spinning apparatus for filaments comprised of polyethylene, polypropylene, or other thermoplastic resins. In this apparatus, a plurality of molten filaments 2 extruded from a die 1 are cooled by cooling air blown from a cooling apparatus 3 and then taken up with a draft. The cooling apparatus 3 comprises a chimney 4 connected to a die 1 in a manner so as to surround the molten filaments 2 and a gas temperature adjustment apparatus 5 composed of coolers. The apparatus 5 cools the cooling air to the desired temperature and the cooling air is fed to the chimney 4 by a fan 6 and is blown from the inner peripheral surface thereof through a filter 7. Reference numeral 8 is an exhaust fan.
In the cooling of molten filaments, if the temperature of the cooling air is lowered or the air flow rate is increased so as to rapidly cool the filaments, only the surface of the filaments will be cooled and solidified. If a draft is applied to the filaments in that state, the filaments will melt and break or the elasticity, tensile strength, and other physical properties of the yarn will be lowered. Conversely, if the filaments are gradually cooled, the filaments tend to adhere to each other and, further, the cooling zone must be made longer, and thus the size of the apparatus is necessarily increased.
Even if the spinning speed is increased or changed, if the cooling is carried out without changing the length of the cooling zone, a rapid cooling becomes necessary, and thus the problems discussed above will arise.